I experienced this lag since my very first game on pc.. Ist not only when aiming, it feels like every 2-3 sec there is a framedrop, it doesnt matter if I am walking or shooting or doing anything else. Also these lags are worse and better from game to game. E.g. in the first game there is almost no lag and in the next I can barely move/aim/shoot.

I dont really know which information are important but here is my DxDiag: